1. Field of the Invention
The present invention relates to process of No. 7 level 2 in a mobile communication switching unit and more particularly to a No. 7 level 2 processing system for a switching unit in mobile communication and method of control thereof, for processing at least one level 2 protocol in real time by implementing a signalling link function corresponding to a level 2 at a message transfer part in a common channel signalling system.
2. Description of Related Art
Generally, a mobile communication system allows communications while in movement using mobile terminals. The mobile communication system includes a personal communication system (PCS) and a digital cellular system (DCS).
Typically, No. 7 signalling system corresponds to the control plane among three multiple planes (the user plane, the control plane, and the management plane) of Integrated Services Digital Network Protocol Reference Model (ISDN-PRM) provided by ISDN architecture based upon International Telecommunications Union, Telecommunication (ITU-T) Recommendation I.320. The No. 7 signalling system is responsible for providing network layer services (layers 1 to 3) of Open System Interconnection (OSI) 7 layers to end-users. The No. 7 signalling system is largely divided into two functions: a network service part (NSP) and a user part (UP). The NSP reliably transmits signalling messages and the UP is a functional entity which uses transmission ability provided by the NSP. The No. 7 signalling system has been developed for usage in digital communication networks and ISDN. It has hierarchical modules, is subjected to a common channel signalling system, and can be applied to an intelligent network such as a communication network contributing to special service. Compared with existing signalling systems, is the No. 7 signalling system can provide a great volume of signal capacity and high speed transmission, improve reliability via error detection and correction, and easily provide other new services (CUG, closed subscribers group, cashless telephone service, wide area receiving service, and so on).
No. 7 protocol hierarchical architecture should be prepared for interlock with other systems using a No. 7 protocol.
As shown in FIG. 1, a typical mobile communication system No. 7 protocol comprises: visitor location register (VLR) 1 which contains information related to the mobile unit's location which has entered the coverage area of mobile switching center (MSC) 2; the MSC 2 for transmitting call process requests from mobile units via public networks or private networks to thereby provide PCS service; ISDN user part 3 for providing ISDN service to subscribers; first and second transaction capability application parts (TCAP) 4 and 5 for processing respective commands from the VLR 1 and MSC 2 and transmitting respective results to signalling connection control part 6; signalling connection control part (SCCP) 6 for controlling connection of signals of the ISDN user part 3 and the first and second TCAPs 4 and 5 to message transfer part (MTP) 7; MTP 7 including level 3, 8, coupled to the ISDN user part 3 and SCCP 6 and consisting of a signalling network management part and a signaling message handling part, for defining procedures and functions related to an operation of transmitting signalling messages between signalling points on the signalling network, level 2, 9, for defining procedures and functions related to an operation of transmitting signalling messages via a single signalling data link, and level 1, 10, for defining physical and electrical properties of the signalling data link, thereby performing transmission of signaling messages.
In the No. 7 protocol architecture having such configuration, the signalling data link (SDL) is used for actual transmission of signalling messages and means a physical path consisting of digital or analog transmission media. The SDL is a bidirectional transmission line comprising two data channels which respectively operate in opposite directions to each other at the same speed. A signalling terminal (ST) allows messages to be reliably transmitted using the signalling data link and is a device for performing all functions defined by the level 2. A signalling link (SL) connects signalling points for the purpose of transmission of signalling messages and comprises the signalling data link and the signalling terminal.
FIG. 2 is a block diagram of a No. 7 level 2 processing system in a conventional mobile communication switching unit. As shown in FIG. 2, the conventional No. 7 level 2 processing system comprises: central processing unit 11 for overall controlling the level 2 processing system; clock generator 12 for generating clocks to the central processing unit 11; reset unit 13 for resetting the central processing unit 11; address encoder and decoder 14 coupled to the central processing unit 11, for encoding and decoding addresses; memory decoder 15 coupled to the central processing unit 11, for generating data transmission and confirm signals and decoding memory; read only memory (ROM) 16 for storing programs which are executed by central processing unit 11; status register 17 which embeds a status register to be processed by central processing unit 11; multi function peripheral (MFP) 18 coupled to central processing unit 11, for controlling peripheral units; direct memory access controller (DMAC) 19 for allowing central processing unit 11 to perform direct memory access to other units in the system; random access memory (RAM) 20 for storing data which has been processed by central processing unit 11; control register 21 for embedding a control register to be processed by central processing unit 11; first and second multi protocol communication controllers (MPCC) 22 and 23 for controlling protocol communications between central processing unit 11 and external units; signalling terminal group bus (STG BUS) matching unit 24 coupled to the first MPCC 21, for performing matching with an STG bus; alarm processing unit 25 for processing alarms generated in the system; and SDL matching unit 26 coupled to the second MPCC 23, for performing matching with SDL.
Such conventional system operates such that one level 2 protocol would be processed in one board. Specifically, by using central processing unit 11 made up of a 16-bit MC68000, MFP 18 made up of an MC68901, DMAC 19 made up of an MC68450, first and second MPCCs 22 and 23 made up of a BT68561 which can process a high-level data link control (HDLC) protocol, and firmware, one level 2 protocol is processed.
FIG. 3 is a flow chart illustrating the operation of a No. 7 level 2 processing system in a mobile communication switching unit according to conventional art. Central processing unit 11 initializes RAM 20 and hardware devices (ST1 and ST2), registers an interrupt service routine address (ST3), and prepares for reception of a message from an upper level (ST4). Central processing unit 11 checks an interrupt flag and receives the input data from the upper level to thereby perform the level 2 protocol defined in recommendations.
Central processing unit 11 then receives messages from the other's signalling link and a signalling message handling processor (SMHP) and transmits messages to the other office and the SMHP (ST5-ST9). Among auxiliary processors having respective various functions in the switching unit, the SMHP is for processing No. 7 messages and refers to a hardware board which actually receives and routes messages.
Once data is transmitted from central processing unit 11 to second MPCC 23, second MPCC 23 processes HDLC frames and sends them to SDL matching unit 26 for transmission. Central processing unit 11 then performs the level 2 protocol. If the processed data is normal and supposed to be sent to the upper level, central processing unit 11 finally sends the data to the upper level via first MPCC 22.
In the conventional system, however, internal circuits are embodied according to TTL (transistor-transistor logic). This causes a problem of requiring a great volume of space in case of processing at least two level 2 protocols within one board.
Additionally, the conventional system processes all level 2 protocols in software using a 16-bit central processing unit, so it needs 21 cycles when the central processing unit performs one command and uses 10 Mhz. Accordingly, the central processing unit needs about 2 microseconds for the process to thereby have performance of 0.5 MIPS (million instruction per second). However, when performing at least two level 2 protocols within one board, delay occurs in processing because volume of data to be processed increases four times. This causes deterioration of performance of the system.